The scientists led by Dr Aaron Robotham of the University of Western Australia examined more than 22,000 galaxies and found that while dwarf galaxies are efficient at creating stars from gas, giant galaxies are much less efficient at star formation and, instead, expand by snacking on their neighbors.
“All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars. Then every now and then they get completely cannibalized by some much larger galaxy,” said Dr Robotham, who is the first author of the paper published in the Monthly Notices of the Royal Astronomical Society.
“Our Milky Way Galaxy hasn’t merged with another large galaxy for a long time but you can still see remnants of all the old galaxies we’ve cannibalized,” he said.
Our Galaxy is going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about 5 billion years. But the nearby Andromeda Galaxy will eat it in about 5 billion years.
“Technically, Andromeda will eat us because it’s the more massive one,” Dr Robotham said.
“As galaxies grew they had more gravity and could therefore more easily pull in their neighbors.”
“Ultimately, gravity is expected to cause all the galaxies in bound groups and clusters to merge into a few super-giant galaxies, although we will have to wait many billions of years before that happens.”
“If you waited a really long time that would eventually happen, but by really long, I mean, many times the age of the Universe so far,” Dr Robotham concluded.